Novel compound, method for producing the same and method for producing fluoropolymer

ABSTRACT

The invention provides a compound which is useful in production of a fluoropolymer and easy to be removed from the produced fluoropolymer, a method of producing the compound, and a method of producing a fluoropolymer using the compound. The invention provides a compound which is represented by Rf 1 —CH 2 O—CF 2 —CHF—Rf 2 —X, wherein Rf 1  represents a fluoroalkyl group containing 1 to 5 carbon atoms, Rf 2  represents a fluoroalkylene group containing 1 to 3 carbon atoms, X represents —COOM or —SO 3 M, and M represents one of H, K, Na, and NH 4 .

TECHNICAL FIELD

The invention relates to a novel compound, a method for producing thenovel compound, and a method for producing a fluoropolymer.

BACKGROUND ART

A carboxylic acid containing a fluoroalkyl group such as ammoniumperfluorooctanoate is thermally and chemically stable. The carboxylicacid can advantageously inhibit a side reaction such as a chain transferwhen used in polymerization reactions, and therefore, it has beenconventionally used as an emulsifier. However, there has been a problemthat conditions for washing, heating and the like for removing thecarboxylic acid from a resin obtained by a polymerization reaction arerestricted within narrow limits.

A method of polymerizing tetrafluoroethylene (TFE) by using a tertiaryperfluoroalkoxide as a surfactant in an aqueous medium, instead of usinga fluorine-substituted carboxylic acid, is known as a method ofproducing a fluoropolymer (see Patent Document 1).

Recently disclosed as other methods of producing a fluoropolymer are amethod of using a carboxylic acid having a fluoroalkyl group and analkylene group containing 1 to 3 carbon atoms as a surfactant (seePatent Document 2), instead of a fluorine-substituted carboxylic acid,and a method of using a carboxylic acid having a fluoroalkyl group andan ether oxygen as a surfactant (see Patent Document 3), instead of afluorine-substituted carboxylic acid.

As a surfactant which is easily removed from a resin obtained bypolymerization, a material including a compound having a —(CF₂O)—structure is suggested (see Patent Document 4)

Patent Document 1: Japanese Kokai Publication S61-207413

Patent Document 2: Japanese Kokai Publication H10-212261

Patent Document 3: U.S. Pat. No. 6,429,258

Patent Document 4: U.S. Patent Application No. 2007/0015864

DISCLOSURE OF INVENTION Problems Which the Invention is to Solve

It is an object of the invention to provide a compound which is usefulin production of a fluoropolymer and easy to be removed from theproduced fluoropolymer, a method of producing the compound, and a methodof producing a fluoropolymer using the compound.

Means for Solving the Problems

The invention provides a compound which is represented by the formula:

Rf¹—CH₂O—CF₂—CHF—Rf²—X

wherein Rf¹ represents a fluoroalkyl group containing 1 to 5 carbonatoms, Rf² represents a fluoroalkylene group containing 1 to 3 carbonatoms, X represents —COOM or —SO₃M, and M represents one of H, K, Na,and NH₄.

The invention provides a method of producing a fluorine-containingcompound comprising the steps of:

(1) adding, to a compound (a1), a compound (a2) in an aqueous mediumunder an alkaline condition to obtain a compound (a3), the compound (a1)represented by CF₂═CF—Rf²—X, wherein Rf² represents a fluoroalkylenegroup containing 1 to 3 carbon atoms, X represents —COOM or —SO₃M, and Mrepresents one of H, K, Na, or NH₄, the compound (a2) represented byRf¹—CH₂OH, wherein Rf¹ represents a fluoroalkyl group containing 1 to 5carbon atoms and the compound (a3) represented byRf¹—CH₂—O—CF₂—CHF—Rf²—X, wherein Rf¹, Rf², and X are as defined above;and(2) fluorinating the compound (a3) to obtain the fluorine-containingcompound, the fluorine-containing compound represented byRf³—O—CF₂—Rf⁴—X, wherein Rf³ represents a fluoroalkyl group containing 1to 6 carbon atoms, Rf⁴ represents a fluoroalkylene group containing 1 to4 carbon atoms, and X is as defined above.

The invention provides a surfactant which includes the above compound ofthe invention.

The invention provides a surfactant for polymerization which includesthe above compound of the invention.

The invention provides a method of producing a fluoropolymer, whichincludes polymerizing a fluoromonomer in an aqueous medium in thepresence of the above compound of the invention.

The invention provides a fluoropolymer aqueous dispersion, whereinfluoropolymer particles having an average particle size of 50 to 500 nmare dispersed in an aqueous medium in the presence of the above compoundof the invention.

The invention provides a method of producing the fluoropolymer aqueousdispersion, which includes the steps of:

(I) contacting an aqueous dispersion of a fluoropolymer with an anionexchange resin in the presence of a nonionic surfactant; and(II) concentrating the aqueous dispersion obtained in the step (I) sothat the aqueous dispersion has a solid content concentration of 30 to70% by mass with respect to 100% by mass of the aqueous dispersion.

The invention provides a fine powder of a fluoropolymer, which isobtained from the above fluoropolymer aqueous dispersion.

The invention provides a fine powder of a fluoropolymer, which isobtained by coagulating the fluoropolymer from the above fluoropolymeraqueous dispersion.

The invention provides a method of recovering a compound, which includesthe steps of:

recovering the above compound of the invention from wastewater and/orgas generated in the step of producing the above fine powder; andpurifying the recovered compound.

In the following, the invention is described in detail.

The compound of the invention is represented by the formula (1):

Rf¹—CH₂O—CF₂—CHF—Rf²—X   (1)

wherein Rf¹ represents a fluoroalkyl group containing 1 to 5 carbonatoms, Rf² represents a fluoroalkylene group containing 1 to 3 carbonatoms, X represents —COOM or —SO₃M, and M represents one of H, K, Na,and NH₄.

The compound of the invention has the following advantages.

The compound has Rf¹ and Rf² each containing the above defined number ofcarbon atoms, and has an acidic group such as —COOM. Accordingly, thecompound is allowed to have excellent dispersibility and is suitablyused as a surfactant, especially as a surfactant for polymerization.

Since the compound has the Rf¹—CH₂O— structure (Rf¹ is as definedabove), when used in the production of a fluoropolymer, the compound iseasily removed from the obtained polymer, which will be described later.In addition, fluorination of the compound provides a fluorine-containingcompound which is excellent in dispersibility when used as anemulsifier.

In the formula (1), Rf¹ is preferably a fluoroalkyl group containing 1to 3 carbon atoms.

Each of Rf¹ and Rf² may have the —CH₂— structure, provided that at leastone fluorine atom is contained. When used as a surfactant forpolymerization, each of Rf¹ and Rf² is preferably a perfluoro group sothat the molecular weight of an obtained polymer is increased. In Rf¹,the carbon atom bound to —CH₂O— preferably contains a fluorine atom.

X is preferably —COOM.

M is preferably NH₄ in terms of good dispersibility.

The step (1) in the method of producing a fluorine-containing compound,which will be specifically described in the following, provides thecompound of the invention as the compound (a3).

The method of producing a fluorine-containing compound of the inventionincludes the step (1) of adding, to the compound (a1), the compound (a2)in an aqueous medium under an alkaline condition to obtain the compound(a3). Here, the compound (a1) is represented by CF₂═CF—Rf²—X (whereinRf² and X are as defined above). The compound (a2) is represented byRf¹—CH₂OH (wherein Rf¹ is as defined above). The compound (a3) isrepresented by Rf¹—CH₂—O—CF₂—CHF—Rf²—X (wherein Rf¹, Rf², and X are asdefined above).

In accordance with the method of producing a fluorine-containingcompound of the invention, the compound (a1) and the compound (a2) arereacted so that the compound (a3) as a novel compound is obtained.

In the production method, preferable examples of Rf¹, Rf² and X in thecompounds (a1) and (a2) are the same as those described for thecomposition of the invention.

In the step (1), the reaction between the compounds (a1) and (a2) can becarried out, for example, at a temperature of 0° C. to 200° C. aftermixing the compounds (a1) and (a2) in a ratio close to thestoichiometric mixture ratio.

The reaction is carried out under an alkaline condition. The alkalinecondition refers to pH 9 or higher. This condition can be set by aconventionally known method, for example, by using an aqueous solutionof an alkaline compound such as KOH.

In accordance with the method of producing a fluorine-containingcompound of the invention, the compound (a3) is fluorinated in the step(2).

The fluorination can be carried out by a conventionally known method,such as a method in which the compound is contacted with fluorine gasand a method in which the compound is extruded under high shear force.The mode of the fluorination reaction can be appropriately selected inaccordance with the number of carbon atoms contained in the compound(a3), a reaction scale of the compound (a3) and the like. The reactionis preferably carried out, for example, under the following conditions.

In the method in which the compound is contacted with fluorine gas,fluorine gas is preferably mixed with inert gas such as nitrogen andhelium and used at a concentration of 10 to 50% by volume.

Fluorine gas is preferably carried out at a temperature of 50° C. to200° C. The contact with fluorine gas is preferably carried out under apressure of 1 kPa to 0.1 MPa.

The method in which the compound is extruded under high shear force isnot particularly restricted. Examples thereof include a method in whichshear force is applied at extruding the compound by using a twin-screwextruder. When the extrusion is conducted, water or air is preferablysupplied in order to efficiently fluorinate the compound.

The above described fluorination carried out in the step (2) providesthe fluorine-containing compound represented by Rf³—O—CF₂—Rf⁴—X (whereinRf³ represents a fluoroalkyl group containing 1 to 6 carbon atoms, Rf⁴represents a fluoroalkylene group containing 1 to 4 carbon atoms, and Xis as defined above).

In the fluorine-containing compound, Rf³ is derived from Rf¹—CH₂— andRf⁴ is derived from —CHF—Rf². They may be fully fluorinated, oralternatively, partially fluorinated. For example, in the case of Rf¹ isCF₃CF₂CF₂—, Rf³ may be CF₃CF₂CF₂CF₂— or CF₃CF₂CF₂CHF—, and further, Rf³may be CF₃CF₂CF₂CH₂—, provided that the other carbon atoms in thecompound are fluorinated.

The fluorine-containing compound exhibits the following excellentproperties.

The fluorine-containing compound is excellent in dispersibility, as thenumbers of carbon atoms and the acidic group contained therein are assame as those in the compound of the invention.

When used in the production of a fluoropolymer, for example, thefluorine-containing compound is easily removed from the obtainedpolymer, as it has the Rf³—O— structure (Rf³ is as defined above).

In accordance with the method of producing a fluoropolymer of theinvention, a fluoromonomer is polymerized in an aqueous medium in thepresence of the above-described compound of the invention (hereinbelow,this compound is referred to as “compound (a)”).

The total additive amount of the compound (a) is preferably 0.0001 to 2%by mass to the mass of the aqueous medium. A more preferable lower limitthereof is 0.001% by mass and a more preferable upper limit thereof is0.5% by mass. At levels below 0.0001% by mass, dispersibility is likelyto be insufficient. While the total additive amount exceeding 2% by masswill produce no further dispersing effect proportional to the additiveamount, leading to lowering of the polymerization rate and stopping thereaction in some cases. The additive amount of the compound (a) isappropriately determined in accordance with the species of afluoromonomer to be used, the molecular weight of the desiredfluoropolymer and the like.

As the fluoromonomer, there may be mentioned, among others,fluoroolefins, preferably fluoroolefins containing 2 to 10 carbon atoms;fluorinated cyclic monomers; and fluorinated alkyl vinyl ethersrepresented by the formula CY₂═CYOR¹ or CY₂═CYOR²OR³ (in which Y is H orF, R¹ and R³ each is an alkyl group containing 1 to 8 carbon atoms asresulting from substitution of a part or the whole of the hydrogen atomsby a fluorine atom or atoms, and R² is an alkylene group containing 1 to8 carbon atoms as resulting from substitution of a part or the whole ofthe hydrogen atoms by a fluorine atom or atoms).

The fluoroolefin preferably contains 2 to 8 carbon atoms. As thefluoroolefin containing 2 to 8 carbon atoms, there may be mentioned, forexample, tetrafluoroethylene [TFE], hexafluoropropylene [HFP],chlorotrifluoroethylene [CTFE], vinyl fluoride, vinylidene fluoride[VDF], trifluoroethylene, hexafluoroisobutylene andperfluorobutylethylene. As the fluorinated cyclic monomer, there maypreferably be mentioned perfluoro-2,2-dimethyl-1,3-dioxole [PDD],perfluoro-2-methylene-4-methyl-1,3-dioxolane [PMD], etc.

Referring to the fluorinated alkyl vinyl ether, each of R¹ and R³preferably contains 1 to 4 carbon atoms and, more preferably, is the oneresulting from substitution of all the hydrogen atoms by fluorine atoms,while R² preferably contains 2 to 4 carbon atoms and, more preferably,is the one resulting from substitution of all the hydrogen atoms byfluorine atoms.

As the fluorine-free monomer, there may be mentioned a hydrocarbonmonomer reactive with the fluoromonomer. As the hydrocarbon monomer,there may be mentioned, among others, alkenes such as ethylene,propylene, butylene and isobutylene; alkyl vinyl ethers such as ethylvinyl ether, propyl vinyl ether, butyl vinyl ether, isobutyl vinyl etherand cyclohexyl vinyl ether; vinyl esters such as vinyl acetate, vinylpropionate, vinyl n-butyrate, vinyl isobutyrate, vinyl valerate, vinylpivalate, vinyl caproate, vinyl caprylate, vinyl caprate, vinylversatate, vinyl laurate, vinyl myristate, vinyl palmitate, vinylstearate, vinyl benzoate, vinyl p-tert-butylbenzoate, vinylcyclohexanecarboxylate, vinyl monochloroacetate, vinyl adipate, vinylacrylate, vinyl methacrylate, vinyl crotonate, vinyl sorbate, vinylcinnamate, vinyl undecylenate, vinyl hydroxyacetate, vinylhydroxypropionate, vinyl hydroxybutyrate, vinyl hydroxyvalerate, vinylhydroxyisobutyrate and vinyl hydroxycyclohexanecarboxylate; alkyl allylethers such as ethyl allyl ether, propyl allyl ether, butyl allyl ether,isobutyl allyl ether and cyclohexyl allyl ether; and alkyl allyl esterssuch as allyl acetate, allyl propionate, allyl butyrate, allylisobutyrate and allyl cyclohexanecarboxylate.

The fluorine-free monomer may also include a functional group-containinghydrocarbon monomer. As the functional group-containing hydrocarbonmonomer, there may be mentioned, for example, hydroxyalkyl vinyl etherssuch as hydroxyethyl vinyl ether, hydroxypropyl vinyl ether,hydroxybutyl vinyl ether, hydroxyisobutyl vinyl ether andhydroxycyclohexyl vinyl ether; carboxyl group-containing, fluorine-freemonomers such as itaconic acid, succinic acid, succinic anhydride,fumaric acid, fumaric anhydride, crotonic acid, maleic acid, maleicanhydride and perfluorobutenoic acid; glycidyl group-containing,fluorine-free monomers such as glycidyl vinyl ether and glycidyl allylether; amino group-containing, fluorine-free monomers such as aminoalkylvinyl ethers and aminoalkyl allyl ethers; and amide group-containing,fluorine-free monomers such as (meth)acrylamide and methylolacrylamide.

The polymerization in the invention is conducted as follows. Apolymerization reactor is charged with an aqueous medium, the compound(a), the fluoromonomer, and other additives (if needed). The mixture inthe polymerization reactor is stirred and the reactor is held at apredetermined polymerization temperature. Then, a polymerizationinitiator is added so as to start the polymerization reaction. After thestart of the polymerization reaction, the fluoromonomer, thepolymerization initiator, a chain transfer agent, and the compound (a)may be additionally added in accordance with the purpose of thereaction.

The aqueous medium is a reaction medium for polymerization and refers toa liquid which contains water. The aqueous medium is not particularlyrestricted, as long as it contains water. Examples thereof may include amedium containing: water; and a fluorine-free organic solvent, such asalcohols, ethers, and ketones, and/or a fluorine-containing organicsolvent having a boiling point of 40° C. or lower.

The polymerization initiator is not particularly restricted, as long asit generates a radical in the above range of the polymerizationtemperature. A known oil-soluble and/or water-soluble polymerizationinitiator may be used. Further, a redox system resulting from combineduse of the polymerization initiator and a reducing agent may be used toinitiate the polymerization. The concentration of the polymerizationinitiator is appropriately determined in accordance with the species ofthe monomer, the molecular weight of the desired polymer, and the rateof reaction.

In accordance with the method of producing a fluoropolymer of theinvention, it is possible to produce a fluoropolymer efficiently byusing at least one of the compounds (a) mentioned above as a surfactant.In carrying out the method of producing a fluoropolymer of theinvention, a certain compound having surfactant activity other than thecompound (a) may also be used simultaneously if it is volatile or theremains thereof in fluoropolymer moldings or the like are allowable.

The other compound having surfactant activity is not particularlyrestricted but may be any of anionic, cationic, nonionic or betaine-typesurfactants, for instance, and these surfactants may be hydrocarbontypes.

In the above polymerization, the polymerization temperature is generally5° C. to 120° C. and the polymerization pressure is generally 0.05 to 10MPaG. The polymerization temperature and polymerization pressure are tobe appropriately selected according to the fluoromonomer speciesemployed, the molecular weight of the desired polymer and the rate ofreaction.

The above polymerization provides a fluoropolymer aqueous dispersioncontaining 5 to 45% by mass of fluoropolymer particles having an averageprimary particle size of 50 to 500 nm.

In the present description, the average primary particle size isobtained indirectly from the transmittance, per unit length of thefluoropolymer aqueous dispersion, of the incident light of 550 nmthrough the fluoropolymer aqueous dispersion adjusted to the solidcontent concentration of the fluoropolymer of 0.22% by mass, based on aworking curve constructed by plotting such transmittance data againstthe average primary particle size obtained from a transmission electronmicroscopy photomicrograph.

The concentration of the fluoropolymer particles is obtained as follows.An amount of 1 g of the aqueous dispersion is dried in an air dryer at150° C. for 60 minutes and the proportion of the mass of nonvolatilecontent with respect to the mass (1 g) of the aqueous dispersion wasobtained and expressed as a percentage.

The fluoropolymer is the one obtained by polymerizing the fluoromonomerand, in accordance with the intended purpose, the fluorine-free monomermay be copolymerized with the fluoropolymer.

As a fluoropolymer suitably producible by the production methodaccording to the invention, there may be mentioned TFE polymers in whichthe monomer showing the highest mole fraction (hereinafter, “mostabundant monomer”) among the monomers constituting the polymer is TFE,VDF polymers in which the most abundant monomer is VDF, CTFE polymers inwhich the most abundant monomer is CTFE, and so forth.

The TFE polymer may suitably be a polytetrafluoroethylene (PTFE) polymersuch as TFE homopolymers, a copolymer derived from (1) TFE; (2) one ormore fluoromonomers other than TFE containing 2 to 8 carbon atoms, inparticular HFP or CTFE, and/or (3) some other monomers. As the othermonomers (3), there may be mentioned, for example, fluoro(alkyl vinylether) species containing 1 to 5 carbon atoms, in particular 1 to 3carbon atoms; fluorodioxoles; perfluoroalkylethylenes; andω-hydroperfluoroolefins.

The TFE polymer may further be a copolymer of TFE and one or morefluorine-free monomers. As the fluorine-free monomer, there may bementioned, for example, alkenes such as ethylene and propylene; vinylesters; and vinyl ethers. The TFE polymer may further be a copolymerderived from TFE, one or more fluoromonomers containing 2 to 8 carbonatoms, and one or more fluorine-free monomers.

The VDF polymer may suitably be a VDF homopolymer [PVDF] or a copolymerderived from (1) VDF, (2) one or more fluoroolefins other than VDFcontaining 2 to 8 carbon atoms, in particular TFE, HFP and/or CTFE, and(3) a perfluoro(alkyl vinyl ether) having an alkyl group containing 1 to5 carbon atoms, in particular 1 to 3 carbon atoms, among others.

The CTFE polymer may suitably be a CTFE homopolymer or a copolymerderived from (1) CTFE, (2) one or more fluoroolefins other than CTFEcontaining 2 to 8 carbon atoms, in particular TFE and/or HFP, and (3) aperfluoro(alkyl vinyl ether) containing an alkyl group containing 1 to 5carbon atoms, in particular 1 to 3 carbon atoms.

The CTFE polymer may also be a copolymer derived from CTFE and one ormore fluorine-free monomers. Included among the fluorine-free monomersare alkenes such as ethylene and propylene; vinyl esters; and vinylethers.

In the production method according to the invention, after theabove-described polymerization, an obtainable fluoropolymer may besubjected to concentration or dispersion stabilization so that anaqueous dispersion thereof is prepared, or alternatively, thefluoropolymer may be recovered by coagulation or flocculation and driedso that a powder or other solid forms are prepared.

As a method of concentration, a known method such as phase separation,electrical isolation and ultrafiltration may be mentioned. Theconcentration can adjust the fluoropolymer concentration to 30% to 70%by mass. The stability of the dispersion may be impaired uponconcentration but, in such a case, a dispersion stabilizer may befurther added. The above-mentioned compound (a) or any of varioussurfactants may be added as the dispersion stabilizer. The variousdispersion stabilizers include, but are not limited to, nonionicsurfactants such as polyoxyalkyl ethers, in particular polyoxyethylenealkylphenyl ethers (e.g. Triton X-100 (trademark), product of Rohm &Haas), and polyoxyethylene isotridecyl ether, polyoxyethyleneisotridecyl ether (NOIGEN TDS80C (trademark), product of DAI-ICHI KOGYOSEIYAKU CO., LTD.; LEOCOL TD90D (trademark), product of LIONCorporation; GENAPOL X080 (trademark), product of Clariant (Japan)K.K.).

The total amount of the dispersion stabilizers corresponds to aconcentration of 0.5 to 20% by mass relative to the solids content ofthe dispersion. At levels below 0.5% by mass, the dispersion stabilitymay be poor in certain cases, while the total amount exceeding 20% bymass will produce no further dispersing effect proportional to theirabundance, hence are impractical. A more preferred lower limit to thetotal amount of the dispersion stabilizers is 2% by mass, and a morepreferred upper limit is 12% by mass.

The aqueous dispersion obtained by carrying out the polymerizationmentioned above, without concentration, can be subjected to dispersionstabilization treatment according to the intended use thereof so that afluoropolymer aqueous dispersion with a long pot life may be prepared.As the dispersion stabilizer to be used, there may be mentioned the sameones as those mentioned hereinabove.

A fluoropolymer producible by the production method according to theinvention can be a glass, plastic, or elastomeric fluoropolymer. Theseare amorphous or partially crystalline, and can be subjected tocompression sintering processing, melt processing, or non-meltprocessing.

The production method according to the invention can suitably be appliedto the production of, for example, polytetrafluoroethylene polymers [TFEpolymers] as non-melt processible resins (I), ethylene/TFE copolymers[ETFEs], TFE/HFP copolymers [FEPs] and TFE/perfluoro(alkyl vinyl ether)copolymers [PFAs, MFAs, etc.] as melt processible resins (II) and, aselastomeric copolymers (III), TFE/propylene copolymers,TFE/propylene/third monomer copolymers (the third monomer being VDF,HFP, CTFE, a perfluoro(alkyl vinyl ether) or the like),TFE/perfluoro(alkyl vinyl ether) copolymers; HFP/ethylene copolymers,HFP/ethylene/TFE copolymers; PVDF; VDF/HFP copolymers, HFP/ethylenecopolymers, VDF/TFE/HFP copolymers and like thermoplastic elastomers;and fluorine-containing segmented polymers described in Japanese PatentPublication (Kokoku) S61-49327.

The perfluoro(alkyl vinyl ether) referred to above is represented by theformula:

Rf⁵(OCFQ¹CF₂)_(k1)(OCR⁴Q²CF₂CF₂)_(k2)(OCF₂)_(k3)OCF═CF₂

wherein Rf⁵ represents a perfluoroalkyl group containing 1 to 6 carbonatoms; k1, k2 and k3 are the same or different and each represents aninteger of 0 to 5; Q¹, Q² and R⁴ are the same or different and eachrepresents F or CF₃.

The above-mentioned non-melt processible resins (I), melt processibleresins (II) and elastomeric polymers (III) suitably producible by themethod of producing a fluoropolymer according to the invention arepreferably produced in the following manner.

(I) Non-Melt Processible Resin

In carrying out the production method of the TFE polymer of theinvention, the polymerization for producing the TFE polymer is generallycarried out at a polymerization temperature of 10 to 100° C. and apolymerization pressure of 0.05 to 5 MPa.

In the above polymerization, a pressure-resistant reaction vesselequipped with a stirrer is charged with pure water and the compound (a)of the invention and, after deoxygenation, further charged with TFE, thetemperature is raised to a predetermined level, and a polymerizationinitiator is added to initiate the reaction. Since otherwise thepressure lowers with the progress of the reaction, an additionalquantity of TFE is fed to the reaction vessel continuously orintermittently so as to maintain the initial pressure. After completionof feeding of a predetermined amount of TFE, the feeding is stopped, theTFE remaining in the reaction vessel is purged, and the temperature isreturned to room temperature. The reaction is thus finished.

In the present specification, the term “polytetrafluoroethylene polymer[TFE polymer]” conceptually includes not only TFE homopolymers but alsothose copolymers of TFE and a modifying monomer(s) which arenon-melt-processible (hereinafter referred to as “modified PTFEs”).

In the production of the TFE polymer, various modifying monomers may beused.

As the modifying monomers, there may be mentioned, among others,perhaloolefins such as HFP and CTFE; fluoro(alkyl vinyl ether) specieshaving an alkyl group containing 1 to 5, in particular 1 to 3, carbonatoms; fluorinated cyclic monomers such as fluorodioxole;perhaloalkylethylenes; and ω-hydroperhaloolefins. The modifying monomerfeeding may be carried out initially all at once, or continuously, orintermittently in portions, according to the intended purpose and thefeeding of TFE.

The modifying monomer content in the modified PTFEs is generally withinthe range of 0.001 to 2 mole percent.

In producing the TFE polymer, persulfate salts (e.g. ammoniumpersulfate) or organic peroxides such as disuccinoyl peroxide anddiglutaroyl peroxide may be used as the polymerization initiator, eithersingly or in the form of a mixture of these. These may also be used incombination with a reducing agent such as sodium sulfite to give redoxsystems. Further, during polymerization, the radical concentration inthe system can be adjusted by adding a radical scavenger such ashydroquinone or catechol or a peroxide-decomposing agent such asammonium sulfite.

In producing the TFE polymer, use can be made of any of the known chaintransfer agents, for example saturated hydrocarbons such as methane,ethane, propane and butane, halogenated hydrocarbons such aschloromethane, dichloromethane and difluoromethane, alcohols such asmethanol and ethanol, and hydrogen. Those which are gaseous at ordinarytemperature and ordinary pressure are preferred. The chain transferagent is generally used in an amount of 1 to 1000 ppm, preferably 1 to500 ppm, relative to the total feed of TFE.

In producing the TFE polymer, use can further be made, as a dispersionstabilizer for the reaction system, of 2 to 10 parts by mass, per 100parts by mass of the aqueous medium, of a saturated hydrocarbon whichcontains not less than 12 carbon atoms, is substantially inert to thereaction and occurs as a liquid under the reaction conditions mentionedabove. Furthermore, ammonium carbonate, ammonium phosphate or the likemay be added as a buffering agent for adjusting the pH during reaction.

At the time of completion of the polymerization of the TFE polymers,aqueous dispersions having a solid content concentration of 10 to 50% bymass and including TFE polymer particles having an average particle sizeof 0.05 to 0.5 μm or, in particular when the compound (a) is used,including very small TFE polymer particles not larger than 0.3 μm insize can be obtained. The TFE polymers at the time of completion of thepolymerization have a number average molecular weight of 1,000 to10,000,000.

The aqueous TFE polymer dispersion obtained by the above-mentionedpolymerization, when supplemented with a nonionic surfactant, isstabilized and, after further concentration, is preferably used invarious fields of application in the form of a composition supplementedwith an organic or inorganic filler(s) according to the intendedpurpose. The above composition, when applied to metal or ceramicsubstrates, can give coated surfaces having nonstickiness and a lowcoefficient of friction and excellent in gloss, wear resistance, weatherresistance and heat resistance. Thus, it is suited for use in coatingrolls and cooking utensils and impregnating processing of glass cloths.

The above-mentioned TFE polymer aqueous dispersion or the fine powdermentioned below is also preferably used as a processing aid. In the caseof use thereof as a processing aid, the aqueous dispersion or finepowder mentioned above is admixed with a host polymer, for instance,whereby the host polymer is improved in melt strength on the occasion ofmelt processing thereof and/or the resulting polymer compositionobtained may show improvements in mechanical strength, electricalcharacteristics, flame retardancy, anti-dripping performance and slidingproperty.

The TFE polymer aqueous dispersion or the fine powder mentioned below isalso preferably used as the processing aid in the form of a compositematerial together with a resin other than the TFE polymer. The TFEpolymer aqueous dispersion or TFE polymer fine powder is suited for useas a raw material for the production of those PTFEs which are describedin Japanese Kokai Publications H11-49912 and 2003-24693, U.S. Pat. No.5,804,654 and Japanese Kokai Publications H11-29679 and 2003-2980. Theprocessing aid comprising the above-mentioned aqueous dispersion or finepowder is not inferior at all to the processing aids described in therespective publications cited above.

The TFE polymer aqueous dispersion mentioned above is also preferablyprocessed by admixing the same with an aqueous dispersion of amelt-processible fluoropolymer, followed by coagulation, to give aco-coagulated powder. This co-coagulated powder is suited for use as aprocessing aid.

As the melt-processible fluoropolymer, there may be mentioned, forexample, FEP, PFA, ETFE and EFEP resins. Among them, FEPs are preferred.

The fluorine-free resin to which the above co-coagulated powder is to beadded may be in the form of a powder, pellets or an emulsion. Theaddition is preferably carried out under shearing force application bysuch a known method as extrusion kneading or roll kneading from theviewpoint of sufficient mixing up of the respective resins.

The TFE polymer aqueous dispersion mentioned above is also preferablyused as a dust-control treatment agent. This dust-control treatmentagent can be used in the method of inhibiting a dust-emitting substancefrom emitting dust by admixing the aqueous dispersion with thedust-emitting substance and subjecting the resulting mixture tocompression-shearing action at a temperature of 20 to 200° C. to therebyfibrillate the TFE polymer, for example in carrying out the methoddescribed in Japanese Patent No. 2827152 or Japanese Patent No. 2538783.

The dust-control treatment agent mentioned above is suitably used indust control treatment in the fields of building and construction, soilstabilizers, solidifying agents, fertilizers, landfill of incinerationash and hazardous substances, explosion protection, cosmetics and soforth.

The TFE polymer aqueous dispersion mentioned above is also suitably usedas a raw material for obtaining a TFE polymer fiber by dispersionspinning method. The dispersion spinning method is a method of obtainingTFE polymer fibers by admixing the TFE polymer aqueous dispersion withan aqueous dispersion of a matrix polymer, subjecting the resultingmixture to extrusion processing to form an intermediate fibrousstructure and baking the intermediate fibrous structure to thereby causedecomposition of the matrix polymer and sintering of TFE polymerparticles.

It is also possible to produce a high-molecular-weight PTFE using thecompound (a) mentioned above. The high-molecular-weight PTFE powderobtained by emulsion polymerization is also useful as a raw material forproducing a porous PTFE article (membrane). For example, a porous PTFEarticle (membrane) can be obtained by subjecting thehigh-molecular-weight PTFE powder to paste extrusion, followed byrolling, and stretching the rolled intermediate product in a non-bakedor half-baked condition in at least one direction (preferably stretchingit by rolling in the direction of rolling, followed by stretching on atenter in the width direction). Stretching makes the PTFE easy tofibrillate and give a porous PTFE article (membrane) consisting of knotsand fibers.

This porous PTFE article (membrane) is useful as a filter for variouspurposes and can be suitably used as a filter for liquid chemicals andas an air filter medium, in particular.

It is also possible to polymerize a low-molecular-weight PTFE using thecompound (a) mentioned above.

The low-molecular-weight PTFE species having a molecular weight of600,000 or below (also called PTFE micropowders) are excellent inchemical stability and very low in surface energy and, in addition,hardly fibrillate and, therefore, are suited for use as an additive forachieving improvements in lubricant properties and/or in coat surfacetexture in manufacturing plastic products, inks, cosmetics, coatings,greases and so forth (cf. e.g. Japanese Kokai Publication H10-147617).

The low-molecular-weight PTFE may also be obtained by dispersing thepolymerization initiator and the above-mentioned compound (a) as anemulsifier in the aqueous medium in the further presence of the chaintransfer agent, followed by polymerizing TFE or TFE and a monomer(s)copolymerizable therewith in the resulting medium.

In the case of using the low-molecular weight PTFE obtained by emulsionpolymerization in the forms of powder, the aqueous dispersion may becoagulated to obtain a powder particle (micro powder).

An unbaked tape (unsintered tape) can also be obtained from the finePTFE powder obtained by using the compound (a) mentioned above.

(II) Melt-Processible Resin

(1) In the production method of the invention, the polymerization forproducing FEP is generally preferably carried out at a polymerizationtemperature of 60 to 100° C. and a polymerization pressure of 0.7 to 4.5MPa.

The monomer composition (on the % by mass basis) of the FEP ispreferably TFE:HFP=(60 to 95):(5 to 40), more preferably (85 to 90):(10to 15). The FEP may be ones modified with a perfluoro(alkyl vinyl ether)as a third component used in a proportion within the range of 0.5 to 2%by mass of the total amount of the monomers.

In the above-mentioned FEP production by polymerization, such a chaintransfer agent as cyclohexane, methanol, ethanol, carbon tetrachloride,chloroform, methylene chloride or methyl chloride is preferably used,and such a pH buffering agent as ammonium carbonate or disodiumhydrogenphosphate is preferably used.

(2) In the production method of the invention, the polymerization forproducing a TFE/perfluoro(alkyl vinyl ether) copolymer, such as PFA andMFA copolymers, is preferably carried out generally at a polymerizationtemperature of 60 to 100° C. and a polymerization pressure of 0.7 to 2.5MPaG. Preferred as the monomer composition (in mole percent) for theTFE/PAVE copolymer is TFE:PAVE=(95 to 99.7):(0.3 to 5), more preferably(98 to 99.5):(0.5 to 2). Preferably used as the PAVEs are thoserepresented by the formula: CF₂═CFORf (in which Rf is a perfluoroalkylgroup containing 1 to 6 carbon atoms).

In the above-mentioned TFE/PAVE copolymer production by polymerization,such a chain transfer agent as cyclohexane, methanol, ethanol, carbontetrachloride, chloroform; methylene chloride, methyl chloride, methaneor ethane is preferably used, and such a pH buffering agent as ammoniumcarbonate or disodium hydrogenphosphate is preferably used.

(3) In the production method of the invention, the polymerization forproducing the ETFE copolymer is generally preferably carried out at apolymerization temperature of 20 to 100° C. and a polymerizationpressure of 0.5 to 0.8 MPaG.

Preferred as the monomer composition (in mole percent) of the ETFE isTFE:ethylene=(50 to 99):(50 to 1). The ETFE may be those modified with athird monomer in a proportion within the range of 0 to 20% by mass ofthe total amount of the monomers. The ratio is preferablyTFE:ethylene:third monomer=(63 to 94):(27 to 2):(4 to 10). Preferred asthe third monomer is perfluoro(butylethlene), perfluoro(butylethlene),2,3,3,4,4,5,5-heptafluoro-1-pentene (CH₂═CFCF₂CF₂CF₂H) and2-trifluoromethyl-3,3,3-trifluoropropene ((CF₃)₂C═CH₂).

In the ETFE production by polymerization, such a chain transfer agent ascyclohexane, methanol, ethanol, carbon tetrachloride, chloroform,methylene chloride or methyl chloride is preferably used.

(4) By utilizing the fluoropolymer production method of the invention,it is also possible to produce an electrolyte polymer precursor. Theelectrolyte polymer precursor production by polymerization according tothe fluoropolymer production method of the invention is preferablycarried out at a polymerization temperature of 20 to 100° C. and apolymerization pressure of 0.3 to 2.0 MPaG. The electrolyte polymerprecursor is a precursor which comprises such a vinyl ether monomer asspecified below and is capable of being converted to an ion-exchangepolymer via a hydrolysis treatment step.

As the vinyl ether monomer to be used in the electrolyte polymerprecursor, there may be mentioned fluoromonomers represented by theformula:

CF₂═CF—O—(CF₂CFY¹—O)_(n)—(CFY²)_(m)-A

wherein Y¹ represents fluorine atom, chlorine atom or a perfluoroalkylgroup, n represents an integer of 0 to 3 and the each of n of Y¹ may bethe same or different, Y² represents fluorine or chlorine atom, mrepresents an integer of 1 to 5 and the each of m of Y² may be the sameor different, and A represents —SO₂X¹ and/or —COZ¹ in which X¹represents a halogen atom and Z¹ represents an alkoxyl group containing1 to 4 carbon atoms. The electrolyte polymer precursor preferably has amonomer composition (mole percent) of TFE:vinyl ether=(50 to 93):(50 to7).

The above-mentioned electrolyte polymer precursor may be the onemodified with a third monomer used in an amount within the range of 0 to20% by mass of the total amount of the monomers.

As the third monomer, there may be mentioned CTFE, vinylidene fluoride,perfluoro(alkyl vinyl ether) species, and divinylbenzene and otherpolyfunctional monomers.

The thus-obtained electrolyte monomer precursor is molded into amembrane shape, for instance, and then subjected to hydrolysis with analkali solution followed by mineral acid treatment for use as a polymerelectrolyte membrane in a fuel cell, among others.

(III) Elastomeric Polymer

In carrying out the polymerization for producing a elastomeric polymeraccording to the method of the invention, a pressure-resistant reactionvessel equipped with a stirrer is charged with pure water and thecompound (a) of the invention and, after deoxygenation, further chargedwith the monomers, the temperature is raised to a predetermined level,and a polymerization initiator is added to initiate the reaction. Sinceotherwise the pressure lowers with the progress of the reaction,additional quantities of the monomers are fed to the reaction vesselcontinuously or intermittently so as to maintain the initial pressure.After completion of feeding of predetermined amounts of the monomers,the feeding is stopped, the monomers remaining in the reaction vesselare purged away, and the temperature is returned to room temperature.The reaction is thus finished. In the case of emulsion polymerization, apolymer latex formed is preferably taken out of the reaction vesselcontinuously.

In particular when a thermoplastic elastomer is to be produced, it isalso possible to employ the method of accelerating the eventual rate ofpolymerization as compared with a conventional polymerizations bysynthesizing fine fluoropolymer particles once in the presence of theabove-mentioned compound (a) at high concentration and, after dilution,further carrying out the polymerization, as disclosed in InternationalPublication WO 00/01741.

In producing the elastomeric polymer, the reaction conditions are to beproperly selected from the viewpoint of desired physical properties ofthe polymer and of a polymerization rate control. For example, thepolymerization is carried out generally at a polymerization temperatureof −20 to 200° C., preferably 5 to 150° C., and generally at apolymerization pressure of 0.5 to 10 MPaG, preferably 1 to 7 MPaG.Preferably, the pH of the polymerization medium is maintained generallyat 2.5 to 9 with a pH adjusting agent, which is to be described laterherein, in a conventional manner, for instance.

As the monomer to be used in producing the elastomeric polymers, theremay be mentioned vinylidene fluoride as well as fluorine-containing,ethylenically unsaturated monomers containing at least the same numberof fluorine atoms as the number of carbon atoms and capable ofcopolymerizing with vinylidene fluoride.

As the fluorine-containing ethylenically unsaturated monomers, there maybe mentioned, among others, trifluoropropene, pentafluoropropene,hexafluorobutene and octafluorobutene. Among them, hexafluoropropene isparticularly suited for use in view of the characteristics of anelastomer obtainable when it blocks the polymer crystal growth. As thefluorine-containing, ethylenically unsaturated monomers, there mayfurther be mentioned trifluoroethylene, TFE, CTFE, etc., andfluorine-containing monomers having one or more chlorine and/or brominesubstituents may also be used. PAVE, for example perfluoro(methyl vinylether), can also be used. TFE and HFP are preferred for the productionof the elastomeric polymer.

The elastomeric polymer preferably has a monomer composition (in % bymass) of vinylidene fluoride:HFP:TFE=(20-70):(30-48):(0-32). Theelastomeric polymer the composition of which is within this range showsgood elastomer characteristics, chemical resistance and thermalstability.

In the polymerization of the elastomeric polymer, any of inorganicradical polymerization initiators known in the art can be used as thepolymerization initiator. Those water-soluble inorganic peroxides knownin the art, for example sodium, potassium and ammonium persulfate,perphosphate, perborate, percarbonate and permanganate, are particularlyuseful as the inorganic radical polymerization initiator. The radicalpolymerization initiator can be further activated by a reducing agentsuch as sodium, potassium or ammonium sulfite, bisulfite, metabisulfite,hyposulfite, thiosulfate, phosphite or hypophosphite, or by a readilyoxidizable metal compound such as a ferrous salt, cuprous salt or silversalt. Ammonium persulfate is a suitable inorganic radical polymerizationinitiator, and the combined use of ammonium persulfate and sodiumbisulfite in a redox system is more preferred.

The level of addition of the polymerization initiator is to be properlyselected according to a desired molecular weight of the polymer and therate of the polymerization reaction; generally, it is set at 0.0001 to10% by mass, preferably 0.01 to 5% by mass of the total amount of themonomers.

In the polymerization of the above elastomeric polymers, any of a chaintransfer agent known in the art can be used. In the case of PVDFpolymerization, hydrocarbons, esters, ethers, alcohols, ketones,chlorine compounds, carbonates or the like can be used and, in the caseof a thermoplastic elastomer, hydrocarbons, esters, ethers, alcohols,chlorine compounds, iodine compounds or the like can be used. Amongthem, acetone and isopropyl alcohol are preferred in the case of PVDFpolymerization and, in the case of thermoplastic elastomerpolymerization, isopentane, diethyl malonate and ethyl acetate arepreferred from the viewpoint that the rate of reaction is hardly loweredthereby, and I(CF₂)₄I, I(CF₂)₆I, ICH₂I and like diiodide compounds arepreferred from the viewpoint that the polymer termini can be iodinatedand the polymer can be used as a reactive one.

The chain transfer agent is used generally in an amount of 0.5×10⁻³ to5×10⁻³ mole percent, preferably 1.0×10⁻³ to 3.5×10⁻³ mole percentrelative to the total feed of the monomers.

In the polymerization of the elastomeric polymer, the polymerization ofPVDF can be preferably carried out using a paraffin wax or the like asan emulsion stabilizer, and the polymerization of the thermoplasticelastomer can be preferably carried out using a phosphate salt, sodiumhydroxide, potassium hydroxide or the like as a pH adjusting agent.

At the time when the polymerization is complete, the elastomeric polymerobtained by the production method of the invention generally has anaverage particle diameter of 0.03 to 1 μm, preferably 0.05 to 0.5 μm anda number average molecular weight of 1,000 to 2,000,000; the solidconcentration is 10 to 40% by mass.

The elastomeric polymer obtained by the production method of theinvention can be converted, according to need, to an aqueous dispersionsuited for rubber molding process by adding a dispersion stabilizer suchas a hydrocarbon surfactant, and concentrating, for instance. Theaqueous dispersion is treated by pH adjustment, coagulation, heating,etc. The respective treatments are carried out in the following manner.

The pH adjustment consists in adjusting the pH to 2 or below by adding amineral acid such as nitric acid, sulfuric acid, hydrochloric acid orphosphoric acid and/or a carboxylic acid containing not more than 5carbon atoms and having a pK=4.2 or below, for instance.

The coagulation is carried out by adding an alkaline earth metal salt.As the alkaline earth metal salt, there may be mentioned calcium ormagnesium nitrate, chlorate and acetate.

Either of the pH adjustment and the coagulation may be carried outfirst. Preferably, however, the pH adjustment is carried out first.

After both procedures, the elastomer is washed with an equal volume ofwater to remove the buffer solution, salt and other impurities occurringin slight amounts within the elastomer, followed by drying. The dryingis generally carried out in a drying oven at elevated temperatures ofabout 70 to 200° C. under circulating hot air.

The fluoropolymer aqueous dispersion according to the invention hasfluoropolymer particles having an average primary particle size of 50 to500 nm dispersed in the aqueous medium in the presence of theabove-described compound (a).

The fluoropolymer aqueous dispersion according to the inventionpreferably has a concentration of fluoropolymer particles of 5 to 70% bymass, and more preferably 30 to 70% by mass.

The aqueous dispersion according to the invention preferably containsthe compound of 0.0001 to 2% by mass with respect to the mass of theaqueous medium. A more preferable lower limit of the amount of thecompound contained therein is 0.001% by mass and a more preferable upperlimit thereof is 0.5% by mass.

The fluoropolymer aqueous dispersion according to the invention may bethe dispersion as obtained in the above-described polymerization, or adispersion solution obtained by concentration or dispersionstabilization treatment of this aqueous dispersion. Further, it may beobtained by dispersing powder of the fluoropolymer obtained by aconventionally known method in the aqueous medium in the presence of thecompound (a).

The invention also includes a method of producing the above-mentionedfluoropolymer aqueous dispersion, which includes the step of (I)contacting an aqueous dispersion of a fluoropolymer with an anionexchange resin in the presence of a nonionic surfactant and (II)concentrating the aqueous dispersion obtained in the step (I) so thatthe aqueous dispersion has a solid content concentration of 30 to 70% bymass with respect to 100% by mass of the aqueous dispersion.

The aqueous dispersion used in the step (I) can be prepared bypolymerizing the above-described fluoromonomer, for instance. Contactingwith an anion exchange resin can be carried out by a conventionallyknown method. Further, concentration can be carried out by theabove-described method.

The production method according to the invention preferably includes astep of recovering the aqueous dispersion of the fluoropolymer byseparating the anion exchange resin after the step (I).

A fine powder of the fluoropolymer of the invention is obtained from theabove-mentioned fluoropolymer aqueous dispersion.

The fine powder of the fluoropolymer is obtained by coagulating thefluoropolymer from the above-mentioned fluoropolymer aqueous dispersionand drying, if needed, the obtained fluoropolymer.

The coagulation can be carried out by a conventionally known method.Conditions for the coagulation may be appropriately selected inaccordance with the composition and the amount of the fluoropolymer.

Examples of the coagulation method include a method of diluting thefluoropolymer aqueous dispersion with water to a polymer concentrationof 10 to 20% by mass, adjusting its pH to neutral or alkaline in somecases, and stirring the dispersion more vigorously compared to thestirring during the reaction in the vessel with a stirrer.

In the coagulation, stirring may be conducted while adding as acoagulant a water-soluble organic compound such as methanol and acetone,an inorganic salt such as potassium nitrate and ammonium carbonate, oran inorganic acid such as hydrochloric acid, sulfuric acid and nitricacid. The coagulation may also be carried out continuously by using anin-line mixer and the like.

Addition of a pigment for coloring or various fillers for improvingmechanical characteristics before or during the coagulation can providea fine powder with a pigment or filler, in which the pigment or filleris uniformly mixed.

The drying is carried out by means of vacuum drying, high-frequencywave, hot blast or the like, in a state where the obtained wet powderdoes not flow easily, preferably in a state where the obtained wetpowder is kept standing.

The drying is carried out at a drying temperature of 10° C. to 250° C.,preferably at 100° C. to 200° C.

The friction between powders especially at a high temperature generallyhas an adverse effect on a fine powder-type PTFE polymer. The reason forthis is that the particle comprising PTFE polymers of this type iseasily fibrillated by applying even low shear force and loses theoriginal state of a stable particle structure.

The fine powder according to the invention preferably has an averageparticle size of 300 to 700 μm.

The average particle size is measured in conformity with ASTM D-1457.

The fine powder preferably has an apparent density of 0.35 to 0.65 g/ml.

The apparent density is measured in conformity with JIS K-6891.

The invention also includes a method of recovering the compound (a),which includes the steps of recovering the compound (a) from wastewaterand/or gas generated in the step of producing the fine powder, andpurifying the recovered compound (a).

The recovering and purifying can be carried out by conventionally knownmethods.

The uses of the fluoropolymer obtained by the production method of theinvention are not particularly restricted but, when it is applied as theaqueous dispersion, the following uses may be mentioned among others:coating of a substrate which comprises applying it to the substrate anddrying the coatings, if necessary followed by baking; impregnationprocess which comprises impregnating a porous support, such as nonwovenfabrics, resin moldings and other porous supports, with the dispersion,followed by drying, if necessary further followed by baking; and castfilm formation which comprises applying the dispersion onto a substratesuch as a glass, drying the coated substrate and, if necessary afterimmersion in water, peeling off the coating from the substrate to give athin film or membrane In these applications, the dispersion is used asan aqueous dispersion type coating composition, an electrode binder, ora water repellent composition for electrodes, for instance.

The fluoropolymer in the form of the aqueous dispersion can be used asan aqueous coating composition after incorporation of one or more knownformulating ingredients selected from among pigments, thickening agents,dispersing agents, antifoaming agents, antifreezing agents, film-formingauxiliaries and the like and/or further compounding of another polymericcompound.

The fine powder of the fluoropolymer is preferably used as a moldingmaterial. Suitable applications of such a fine powder include hydraulic-or fuel-system tubes in air crafts and vehicles, a flexible hose forchemicals or steam, and wire coating applications.

EFFECTS OF THE INVENTION

The compound according to the invention is useful in producing afluoropolymer.

BEST MODES FOR CARRYING OUT THE INVENTION

The following synthesis examples and working examples will illustratethe invention. These synthesis examples and working examples are,however, by no means limitative of the scope of the invention.

The methods used for the measurements in the respective examples areshown below.

Solid content concentration: Determined based on the weight loss after 1hour of drying of each aqueous dispersion at 150° C.Standard specific gravity (SSG): Measured according to ASTM D-1457-69.Average primary particle size: Determined indirectly from thetransmittance, per unit length of the dispersion, of the incident lightof 550 nm through the dispersion diluted to a solid contentconcentration of about 0.02% by mass based on a working curveconstructed by plotting such transmittance data against the averageparticle size data obtained from electron photomicrographs.

SYNTHESIS EXAMPLE 1

A 100-mL three-necked glass flask equipped with a reflux tube andthermometer was charged with 40 g of 15% KOH aqueous solution. Understirring, 17.6 g of CF₂═CFCF₂COOH (disclosed in Japanese PatentPublication S58-52700 (Kokoku)) was added to the solution dropwise toprepare a 37% aqueous solution of CF₂═CFCF₂COOK.

Subsequently, 15 g of CF₃CF₂CH₂OH was added to the solution dropwise andthe inside temperature was maintained at 80° C. Three hours later, thedisappearance of a peak of CF₃CF₂CH₂OH was confirmed by using gaschromatography [GC] and reaction was terminated. Further, after coolingthe solution to room temperature, pH was adjusted to 1 by using anexcess of HCl and the solution was separated to an oil phase and anaqueous phase. Then, the oil phase was recovered and washed withdeionized water to obtain 30 g of CF₃CF₂CH₂OCF₂CFHCF₂COOH. This wasneutralized with ammonia water to obtain CF₃CF₂CH₂OCF₂CFHCF₂COONH₄.

SYNTHESIS EXAMPLE 2

A 100-ml PFA-made vessel equipped with a gas inlet pipe was charged with20 g of the CF₃CF₂CH₂OCF₂CFHCF₂COOH prepared in Synthesis Example 1, andnitrogen was passed through the vessel at a flow rate of 20 ml/minutefor 10 minutes to eliminate oxygen and moisture from the system.Fluorine gas diluted to 24% with nitrogen was passed through the vesselwarmed on a water bath at 60° C. at a flow rate of 40 ml/minute for 16hours. After substitution of the vessel inside atmosphere with nitrogen,19 g of the reaction product was recovered.

This reaction product was rectified at 1.0×10⁴ Pa to give a fraction 1(boiling point 60° C.) and a fraction 2 (boiling point 78° C.).

NMR analysis clarified that the fraction 1 was CF₃CF₂CF₂OCF₂CF₂CF₂COOHand the fraction 2 was CF₃CF₂CHFOCF₂CHFCF₂COOH. These were neutralizedwith ammonia so that CF₃CF₂CF₂OCF₂CF₂CF₂COONH₄ andCF₃CF₂CHFOCF₂CHFCF₂COONH₄ were obtained.

EXAMPLE 1 Preparation of PTFE Latex

A 3-L stainless steel autoclave equipped with a stirring blade wascharged with 1.5 L of deionized water, 60 g of paraffin wax (meltingpoint 60° C.) and 1.5 g of CF₃CF₂CF₂OCF₂CF₂CF₂COONH₄, and the systeminside was substituted with TFE. The inside temperature was raised to70° C., TFE was fed under pressure to an inside pressure of 0.78 MPa,and 3.75 g of a 1% (by mass) aqueous solution of ammonium persulfate[APS] was fed to initiate the reaction. To compensate the pressurereduction in the polymerization system with the progress of thepolymerization, TFE was continuously fed to maintain the inside pressureat 0.78 MPa and, in this manner, the reaction was continued. At 7.5hours after the start of polymerization, TFE was purged away toterminate the polymerization. The solid content concentration of theaqueous dispersion obtained was 30.2% by mass, the standard specificgravity was 2.210, and the average primary particle size of thefluorine-containing polymer was 280 nm.

EXAMPLE 2 Preparation of PTFE Latex

The reaction was carried out in the same manner as in Example 1, exceptthat CF₃CF₂CF₂OCF₂CF₂CF₂COONH₄ in Example 1 was changed toCF₃CF₂CHFOCF₂CHFCF₂COONH₄ obtained in Synthesis Example 2. At 6.2 hoursafter the start of polymerization, TFE was purged away to terminate thepolymerization. The solid content concentration of the aqueousdispersion obtained was 32.1% by mass, the standard specific gravity was2.196, and the average primary particle size of the fluorine-containingpolymer was 250 nm.

INDUSTRIAL APPLICABILITY

The compound according to the invention is useful as a surfactant or anintermediate to produce a surfactant.

1. A compound which is represented by the formula (1):Rf¹—CH₂O—CF₂—CHF—Rf²—X   (1) wherein Rf¹ represents a fluoroalkyl groupcontaining 1 to 5 carbon atoms, Rf² represents a fluoroalkylene groupcontaining 1 to 3 carbon atoms, X represents —COOM or —SO₃M, and Mrepresents one of H, K, Na, and NH₄.
 2. The compound according to claim1, wherein Rf¹ is a fluoroalkyl group containing 1 to 3 carbon atoms. 3.The compound according to claim 1, wherein X is —COOM.
 4. A surfactantwhich comprises the compound according to claim
 1. 5. A surfactant forpolymerization which comprises the compound according to claim
 1. 6. Amethod of producing a fluorine-containing compound comprising the stepsof: (1) adding, to a compound (a1), a compound (a2) in an aqueous mediumunder an alkaline condition to obtain a compound (a3), the compound (a1)represented by CF₂═CF—Rf²—X, wherein Rf² represents a fluoroalkylenegroup containing 1 to 3 carbon atoms, X represents —COOM or —SO₃M, and Mrepresents one of H, K, Na, or NH₄, the compound (a2) represented byRf¹—CH₂OH, wherein Rf¹ represents a fluoroalkyl group containing 1 to 5carbon atoms and the compound (a3) represented byRf¹—CH₂—O—CF₂—CHF—Rf²—X, wherein Rf¹, Rf², and X are as defined above;and (2) fluorinating the compound (a3) to obtain the fluorine-containingcompound, the fluorine-containing compound represented byRf³—O—CF₂—Rf⁴—X, wherein Rf³ represents a fluoroalkyl group containing 1to 6 carbon atoms, Rf⁴ represents a fluoroalkylene group containing 1 to4 carbon atoms, and X is as defined above.
 7. The method of producing afluorine-containing compound according to claim 6, wherein Rf¹ in thecompound (a2) is a fluoroalkyl group containing 1 to 3 carbon atoms. 8.A method of producing a fluoropolymer, which comprises polymerizing afluoromonomer in an aqueous medium in the presence of the compoundaccording to claim
 1. 9. The method of producing a fluoropolymeraccording to claim 8, wherein the polymerization is conducted in thepresence of 0.0001 to 2% by mass of the compound with respect to themass of the aqueous medium.
 10. A fluoropolymer aqueous dispersion,wherein fluoropolymer particles having an average particle size of 50 to500 nm are dispersed in an aqueous medium in the presence of thecompound according to claim
 1. 11. The fluoropolymer aqueous dispersionaccording to claim 10, wherein the concentration of the fluoropolymerparticles is 5 to 70% by mass.
 12. The fluoropolymer aqueous dispersionaccording to claim 10, wherein the amount of the compound represented bythe formula (1) is 0.0001 to 2% by mass with respect to the mass of theaqueous medium.
 13. A method of producing the fluoropolymer aqueousdispersion according to claim 10, which comprises the steps of: (I)contacting an aqueous dispersion of a fluoropolymer with an anionexchange resin in the presence of a nonionic surfactant; and (II)concentrating the aqueous dispersion obtained in the step (I) so thatthe aqueous dispersion has a solid content concentration of 30 to 70% bymass with respect to 100% by mass of the aqueous dispersion.
 14. A finepowder of a fluoropolymer, which is obtained from the fluoropolymeraqueous dispersion according to claim
 10. 15. A fine powder of afluoropolymer, which is obtained by coagulating the fluoropolymer fromthe fluoropolymer aqueous dispersion according to claim
 10. 16. A methodof recovering a compound, which comprises the steps of: recovering acompound represented by the formula (1):Rf¹—CH₂O—CF₂—CHF—Rf²—X   (1) wherein Rf¹ represents a fluoroalkyl groupcontaining 1 to 5 carbon atoms, Rf² represents a fluoroalkylene groupcontaining 1 to 3 carbon atoms, X represents —COOM or —SO₃M, and Mrepresents one of H, K, Na, and NH₄, from wastewater and/or gasgenerated in producing a fine powder obtained from a fluoropolymeraqueous dispersion comprising particles having an average particle sizeof 50 to 500 nm dispersed in an aqueous medium in the presence of thecompound represented by the formula (1); and purifying the recoveredcompound.
 17. A method of recovering a compound, which comprises thesteps of: recovering a compound represented by the formula (1):Rf¹—CH₂O—CF₂—CHF—Rf²—X   (1) wherein Rf¹ represents a fluoroalkyl groupcontaining 1 to 5 carbon atoms, Rf² represents a fluoroalkylene groupcontaining 1 to 3 carbon atoms, X represents —COOM or —SO₃M, and Mrepresents one of H, K, Na, and NH₄, from wastewater and/or gasgenerated in producing a fine powder obtained by coagulating afluoropolymer from a fluoropolymer aqueous dispersion comprisingparticles having an average particle size of 50 to 500 nm dispersed inan aqueous medium in the presence of the compound represented by theformula (1); and purifying the recovered compound.